Scanners, digital copiers, fax machines and the like, commonly use contact image sensors (CIS) for scanning information written on various documents. CIS's generally include a glass window (CIS window), through which an image sensor scans the document. In order to achieve an accurate document scan, the document must be in close proximity to or “contact” the glass window. The optics of the image sensor are designed to achieve peak focus at the surface of the CIS window. Thus, the document must be in good contact with the CIS window to ensure scanning accuracy.
As noted, tight tolerances are required on the distance between the document and the CIS. To achieve this, flatbed scanners and copiers include large windows against which a document lies and a cover or lid closes over the document pushing the document flat against the window. The cover generally includes a foam compliant pad for urging the document into contact with the window. However, scanners and copiers having document feed capability cannot use static pad force to ensure proper contact between the document and the window. Such devices generally include a system of belt and driven presentation rollers for feeding the document past the CIS. Generally, a roller made of compliant material, or in some cases spring biased, is used and placed above the CIS to bias the passing document into contact with the CIS. Due to the tight tolerancing requirements discussed above, the distance between the roller center and the surface of the CIS window must be fairly precise. Sufficient increase or decrease in the distance between the roller and the scanner will affect the amount of drive force required to feed the document through the device. Further, foam rollers are difficult to maintain as they accumulate debris over time, adversely affecting the performance of the device.
Thus, it is desirable in the industry to provide a low cost, low maintenance presentation apparatus and method for biasing a document into sliding contact with a CIS window. Further, it is desirable to provide a presentation apparatus that improves the overall performance and cost effectiveness of an image-scanning device.